Cat Ringworm

Coty, relaxing on the back of the chair

Cat ringworm is a nasty fungus but its not life threatening
although it threatens your cat's skin health. It is not actually a
worm at all. The name was coined years ago because it often causes
round sores, surrounded by small blisters that look like worms. It
often isn't visible until you start investigating after you find a nasty
red circular mark on yourself....yes, a human can get it.

Ringworm
is a “zoonosis” which means that it is an animal disease that can be
transmitted to humans. However, because humans don’t have fur covering
affected areas it is easier to treat. When kittens have it, you usually
see the classical circular, scaly lesions; but in older cats, the signs
are variable. It isn't life threatening to either the cat or yourself
but it is highly contagious. If you have any suspicions have your cat
checked out right away.

There are a number of skin disorders in a cat that can cause the
same clinical symptoms as ringworm so there are specific diagnostic
procedures to obtain a definitive diagnosis. As a first step your vet
may use an ultraviolet light called a “Woods light”. Under this light,
hairs with ringworm glow a bright green fluorescence.

The Woods light
on its own cannot establish a diagnosis, because not all strains of
ringworm fluoresce, plus there are medications and other substances that
do fluoresce but the light helps a vet choose which hairs to test
further.

The hairs are examined under a microscope, and then placed on a
culture plate to test for any growth of ringworm organisms. Skin
scrapings and scale samples are also cultured. The fungal culture in
the cat usually grows positive within two to four weeks.

If growth
occurs, the spores are taken off the plates, stained, and examined under
a microscope to determine which ringworm organism is involved. A
culture that is positive for ringworm is significant, and warrants
treating the cat. This will facilitate an earlier recovery for your cat
and reduce the chance of transmission to humans and other animals.

Cat ringworm is caused by a family of fungi that are known as dermatophytes,
which translates to “skin loving” and this type of fungal infection is
dematophytosis. These fungi thrive on an animals’ skin. They are not
strictly species-specific, but certain strains tend to live on certain
hosts. The type of ringworm fungus that 95% of the time infects cats is
called Microsporum canis.

The same organism also causes most cases of ringworm in dogs. Occasionally, however, fungi Microsporum gypseum or Trichophyton mentagrophytes
are involved. Most commonly, cats contract the M. canis disease from
another animal that has ringworm.

When fungal organisms invade and grow
in the skin, hair, and nails, they produce microscopic spores. These
spores can contaminate the environment, or be passed directly to another
individual by contact. A feline with cat ringworm is continuously
shedding spore-laden hairs.

One factor that can predispose a cat to developing cat ringworm is age. The
immune system of a kitten is not as mature as that of an adult cat,
hence kittens are more susceptible to infection. A kitten nursing from a
ringworm-infected mother will usually develop ringworm. Skin parasites
such as mites and fleas, can irritate the skin and allow it to be more
susceptible to fungal invasion.

Exposure to ringworm does not always
cause infection. An asymptomatic cat showing no lesions can harbor the
organism on its hair-coat, remaining healthy but spreading the disease to
others.

The skin has a natural defense system against cat ringworm
because the oil glands in the skin produce substances that make it less
hospitable to fungi. Sebum, for example, is an oily substance that
spreads out onto the skin and hair and acts as a chemical barrier to
prevent fungi organisms from invading.

The skin’s normal defenses, along with the usual feline fussy grooming
techniques, help to prevent spores from invading the outer layers of
the skin, hair and nails. When this defense fails… cat ringworm occurs.
If left untreated, infections are usually self-limiting and will
eventually resolve on their own but this can take months or even years.

There are numerous treatments for feline ringworm which include pills,
salves, ointments, shampoos and bathing dips. In time the cat’s immune
system will kill off the fungi but the treatment regimen is usually
determined by a veterinarian on a case-by-case basis.

Once confirmed vets usually prescribe both a topical anti-fungal ointment and an
oral anti-fungal drug. Oral treatment drugs such as Griseofulvin, which
is approved by the FDA for use in dogs and cats, can cause some cats to
react with diarrhea or vomiting etc. so the vet will monitor a cat
closely. Prior to drug therapy your vet will do a complete blood count
and test for FIV and FeLv because some drugs cannot be given to cats
suffering from those viruses.

It is not unusual for drug treatments to
take over a month before all spores are gone. Bathing the cat with an
anti-fungal shampoo, followed by dipping in lime sulfur solution, is a
common topical treatment. The dip solution is left on the body to dry.

The cat should be kept warm until completely dry to prevent
hyperthermia. An Elizabethan collar will protect your cat from licking
an excess amount off of his coat and although lime sulfur is reported to
be safe even in kittens, it is, however, stinky and can be irritating
if ingested in large quantities. Too much licking can cause mouth
ulcers and gastrointestinal upsets. If your cat is light colored, her
coat will be temporarily stained.

It is important to take some
precautions when bathing and dipping a cat. Wear protective eyewear and
rubber gloves. Remove all jewelry because the lime solution can cause
tarnishing and discoloration. There are also other topical products
available. There is also a vaccine for cat ringworm designed to boost
the immune system response of infected adult cats. However, vaccination
does not prevent it, but it can help defeat a pre-existing infection.

Unfortunately curing your infected cat is only half of the battle. The spores can live
in the environment for well over a year so you must clean everything
completely even air ducts. Your vet can recommend a safe disinfectant to
use on bedding, litter pans, scratching posts, grooming tools, rugs,
and any other items your infected cat comes in contact with on a regular
basis. A 1:10 dilution of bleach to water can be used on all
non-porous surfaces. Consultation with your vet is recommended.